Experimental Investigations and Application of Ionic Liquids in Small Self-lubricating Porous Journal Bearings
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Author
Date
2017Type
- Doctoral Thesis
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Abstract
Small, self-lubricated porous journal bearings are widely applied in all kind of
different machinery and applications and produced in enormous quantities.
Their low cost, high resistance with respect to impacts and overload make
them a very important and successful bearing solution to support a rotating
shaft carrying a radial load.
For small journal bearings, supporting shafts with diameters in the range
of mm, as applied in small machines, standard techniques of friction analysis
cannot be used, because the boundary conditions of the specific application
cannot be represented. Due to this, different friction values result when
compared to the real application and the measurements obtained are not
precise enough.
This work addresses systematic investigations of small journal bearings
lubricated with Ionic Liquids, which present a novel generation of fluids
with promising properties and good lubrication performance. A setup was
designed and built so as to represent the application of such bearing systems
in a small electric motor of 20mm in diameter and imposes identical
mechanical boundary conditions as experienced in such motors. A nominal
shaft diameter of 3mm was used for the experiments. The important
parameter of the radial clearance was altered by using precise shafts of different
diameters. The radial loading on the bearings was varied in the range
from 0.2N to 10N.
A novel procedure for calibration allows to take into account deviations
from perfect symmetry, as they are encountered on every part of the mechanical
system. This new calibration allows to significantly increase measurement
precision. In the case of miniature bearings, as they are used in
this work, deviations from the ideal geometry cannot be neglected because
measurement precision would suffer dramatically. The setup developed allows for the simultaneous detection of friction and
relative displacement between shaft and bearing, a key parameter in hydrodynamic
lubrication theory. This gives additional insight into the bearing
kinematics and allows to increase the precision of friction measurements even
more, if measured values of shaft-bearing eccentricity are considered for the
calculation of the friction torque. Using the developed setup, a nominal
resolution of 50 nNm could be obtained with displacement measurements
recorded at 150 nm nominal resolution.
An analysis of the displacement signal in the frequency domain was performed
in order to give additional insight into the system dynamics and
detection of whirling phenomena, which typically come along with an increase
in friction. To avoid any misinterpretation of measured friction data,
knowledge of the whirling state is important.
Viscous heating in the lubricant film strongly effects the lubricant temperature
and therefore its viscosity and was also taken into account. Considering
effects of viscous heating is especially important at high speeds.
The setup under test allows for rotational speeds up to 25000 rpm. Using
a combined experimental, numerical and analytical approach, a thermal
model was developed and lubricant temperature and therefore fluid viscosity
can be determined for Stribeck measurements under variation of speed.
Experiments were performed using Newtonian viscosity standards, which
provide constant viscosity over a wide range of shear rates. The effect of
porous bearing material on friction was investigated as well, under variation
of relevant parameters as rotational speed and radial clearance, applying the
corresponding theory and the measurement technique developed.
Several selected Ionic Liquids were applied as lubricant in porous, selflubricating
journal bearings and compared to an established standard lubricant.
Using these new fluids, the measured friction can be described applying
the same models as in the case of the Newtonian reference oil. It was found
that in the domain of mixed lubrication several low viscosity Ionic Liquids
provide lower friction than the highly developed, non-Newtonian standard
lubricant taken as reference. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000245698Publication status
publishedExternal links
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Publisher
ETH ZurichSubject
Stribeck measurement; Journal bearing; Ionic liquids; FRICTION MEASUREMENT (MECHANICS); half-frequency whirling; Experimental investigations; thermohydrodynamic friction modelOrganisational unit
03307 - Dual, Jürg (emeritus) / Dual, Jürg (emeritus)
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ETH Bibliography
yes
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